#160 compilation failure with --enable-fax --disable-statistics

[Mounir Lamouri]

opal fails to compile if configureed with --enable-fax --disable-statistics
It is because OpalMediaStatistics::Fax is used but not defined as it's defined only with --enable-statistics
Adding #ifdef OPAL_STATISTICS around the line is not fixing the failure because m_statistics is highly used in OpalFaxMediaStream::ReadStdOut.
I prefer to let you choose how to manage this instead of writing a stupid patch.

Reproduction:
./configure --enable-fax --disable-statistics
-> compilation failure

[Robert Jongbloed]

Patch applied to Lalande (PTLib 2.6, OPAL 3.6) and trunk, thank you very much!